PRESERVATION OF FISH BY SALT. 5 



cell. It dissolves in some of the moisture, forming a saturateel solu- 

 tion. This solution is separated from the contents of the cell by a 

 cell membrane which is more or less semipermeable. Water passes 

 out of the cell to the salt and the processes of decay are stopped be- 

 cause of insufficiency of water. The membrane, not being absolutely 

 semipermeable, permits some salt to enter and the fish remains salty. 

 The contents left in the cell are proteins or the valuable food ele- 

 ments of the fish which, being colloids, are not permitted by the cell 

 membrane to pass out. Thus water is extracted, salt enters, and the 

 fish is preserved. 



When the time comes to eat the fish the process is exactly reversed. 

 The fish is bathed in pure water. The cell contents are more con- 

 centrated than the exterior, so water passes in. The cell membrane 

 is to some extent semipermeable, so the protein does not escape, but 

 the salt does. This exchange is carried to a point where the meat is 

 again plump and a sufficient quantity of salt has been removed. 



Thus by exposing the meat of fish to salt we have removed the 

 water and caused some salt to enter the meat and have stored the 

 fish. We have then by exposing the fish to water put water back 

 in the cells and taken out the excess salt. The actual food material 

 of the fish — the cell protein — is still where it was, for practical pur- 

 poses unchanged. If every step has been scientifically correct we 

 have at the end very nearly the f re'sh fish we had to start with. But 

 there is the rub. At every turn it is possible to depart from the 

 scientifically correct. The principles of osmosis here very briefly 

 stated are the fundamentals of the art of salting fish. In all that 

 follows there will be frequent occasion to refer to osmosis. 



FACTORS AFFECTING PERMEABILITY OF FISH. 



The preservation of fish by salt is practiced extensively in the 

 cooler j)arts of the United States, but very little has been done south 

 of Chesapeake Bay. The reason fish have not been salted in the 

 warmer parts of the country is that the process has not been satis- 

 factory. Eepeated efforts to salt alewives on the St. Johns Eiver in 

 Florida previous to 1920 uniformly resulted in failure. In 1918 re- 

 search on this problem was undertaken under the immediate direction 

 of the writer. The results of a part of this program were published.^ 



The hypotheses which guided this work were somewhat as follows : 

 During the course of " striking through " the fish two things are 

 happening — (1) the flesh is breaking down by autolysis (a process 

 to be explained later) and (2) the salt is penetrating the flesh. Salt 

 arrests autolysis when it arrives, but considerable damage may be 

 done before the salt has reached the innermost parts of the fish. Now, 

 these two processes — salt penetration and autolysis — are running a 

 race, so to say. If the salt penetrates to the innermost parts before 

 autolysis has destroyed them, the salt wins the race and the fish is 

 saved. If before the salt can get to the innermost parts they have 

 been decomposed by autolysis to an intolerable degree, then autolysis 

 wins and the fish spoils. High temperatures accelerate both proc- 

 esses, but while accurate measurements have not been made we know 



' Tressler, D. K. : Some Considerations Concerning the Salting of Fisli. Appendix IV, 

 Report of the U. S. Commissioner of Fisheries for 1&19, 55 pp. B. F. Doc. No. 884. 

 Washington, 1920. 



